The following publications are believed to represent the state of the art:
U.S. Pat. No. 4,742,215 to Daughters, et al., hereinafter “215”;
U.S. Pat. No. 6,609,114 to Gressel, et. al, hereinafter “114”;
U.S. Pat. No. 6,311,272 to Gressel, et al; and
PCT/IL98/00497 to Tiecher et al describing a stored-value system handling isolated flow and circulation of electronic cash.
The disclosures of all publications mentioned in the specification, and of the publications cited therein directly or indirectly, are hereby incorporated by reference.